Experimental study on the effect of acidity on coal spontaneous combustion at different oxygen concentrations

In order to study the effect of acidity and different oxygen concentration on coal spontaneous combustion under carbon dioxide-oxygen conditions, Changcun coal was investigated by the Thermogravimetry analysis (TG). The combustion characteristics of neutral coal sample and hydrochloric acid coal sample were discussed under oxygen concentration of 20%, 15%, 11.25%, 7.5%, 3.75%, and 2.5%, respectively. The results showed that the TG-DSC curves moved to the high-temperature region, the characteristic temperature increased correspondingly, and the heat release rate became small with the decrease of oxygen concentration. As the temperature increased, the heat release increased rapidly and the difference of heat value between the different oxygen concentrations gradually became larger. At 800 K, the difference of heat release between the maximum and the minimum oxygen concentration was biggest, approximately 11701 J/g for neutral coal and 11510 J/g for acidic coal. At the same oxygen concentration, the heat release of the neutral coal was greater than that of the acidic coal, but it was not obvious when the oxygen concentration was lower than 7.5%. And according to the heat release, critical oxygen concentration of Changcun lean coal was 3.75%.